The statements in this background section may be useful to an understanding of the invention, but may not constitute prior art.
World-wide production of petroleum is expected to peak around year 2020 and decline thereafter which could cause a global economic decline after 2020. Needed are substitute hydrocarbon sources to petroleum. Inventing alternative, large-scale processes for production of hydrocarbons is needed. These processes need to be economical to be incorporated successfully in free market economies. Research is underway to identify substitute processes and feedstocks for these processes that can be used in large-scale production of needed hydrocarbons. Alternative and renewable feedstocks are being explored for use in economical chemical processes to make hydrocarbons such as fuel oil, diesel fuel, kerosene fuel, lubricant base oil and linear alpha olefins. These particular hydrocarbons are currently obtained from processing petroleum.
Some alternative and renewable feedstocks are plant oils, microbial-produced oils and fatty acids, and animal fats. Because microbial-produced fatty acid feedstocks contain acetates and acetic acid in high molar concentrations of 0.3 M to 0.6 M (Kuhry et al., U.S. Pat. No. 8,518,680), the yield of the aforementioned hydrocarbons (fuel oil, diesel fuel, kerosene fuel, lubricant base oil and linear alpha olefins) are very low which indicates that microbial-produced hydrocarbons are not an economically advantageous feedstock. Other prior art teaches the use of a large wt. % of acetic acid. See for example, Weedon et al. (1952); Sumera and Sadain (1990); and Meresz U.S. Pat. No. 4,018,844 (at Col 2:lines 7-10 and in Example 7 in Table I of Col 3-4 which specifically uses acetic acid and oleic acid in a Kolbe electrolysis reaction). Other prior art such as Bradin U.S. Pat. Nos. 7,928,273 and 8,481,771 which teach processes for the production of biodiesel, gasoline and jet fuel start with vegetable oils or animal fat and employ decarboxylation reactions (thermal or Kolbe) of fatty acids, do not mention any use of acetic acid in the decarboxylation reaction.
Feedstocks such as plant oils and animal fats are triglycerides that can be processed using ester hydrolysis, Kolbe electrolysis, olefin metathesis and hydroisomerization to produce fuel oil, diesel fuel, kerosene fuel, lubricant base oil and linear alpha olefins. Ester hydrolysis may be used to convert oils and fats which contain triglycerides to fatty acids. The fatty acids may be decarboxylated and converted into larger hydrocarbons by Kolbe electrolysis. The alkene hydrocarbons produced from Kolbe electrolysis may be reacted by olefin metathesis using catalysts to redistribute the alkenes by a scission and a regeneration of carbon-carbon double bonds. The linear alkene hydrocarbons formed from olefin metathesis using catalysts may be hydroisomerized to add hydrocarbon branches.
There are many plant oils which can be obtained in large amounts from crop plants. Table 1 below indicates the volumetric (liters and gallons) amounts which can be obtained from crops per hectare or acre. Recycled food oils are also being used as a feedstock to produce the aforementioned hydrocarbons.
TABLE 1Amounts of Plant Oils That Have BeenObtained From Various Crop PlantsCropliters oil/hectareUS gal/acrecorn (maize)17218cashew nut17619oats21723lupine23225knead27329calendula30533cotton32535hemp36339soybean44648coffee45949linseed (flax)47851hazelnut48251euphorbia52456pumpkin seed53457coriander53657mustard seed57261camelina58362sesame69674safflower77983rice82888tung oil940100sunflower952102cocoa (cacao)1026110peanut1059113opium poppy1163124rapeseed1190127olive1212129castor bean1413151pecan nut1791191jojoba1818194jatropha1892202macadamia nut2246240brazil nut2392255avocado2638282coconut2689287oil palm5950635
Plant oils and animal fat (such as beef tallow) contain a mixture of triglycerides which can be hydrolyzed to obtain various fatty acids. Most plant oil-derived and animal fat-derived FFAs typically have 10-20 carbon atoms with zero, one, two or three carbon-carbon double bonds.
The Kolbe electrolysis reaction is a chemical reaction process for the decarboxylation of fatty acids in processes making hydrocarbons. The Kolbe electrolysis reaction process may use a single fatty acid or fatty acid mixtures. A significant renewable source of the fatty acids comes from the hydrolysis of triglycerides of plant oils and animal fats.
There are problems in using the Kolbe electrolysis reaction to produce hydrocarbons from fatty acids. The problems include a development of a passivation voltage (a voltage drop at the Kolbe cell electrodes during the Kolbe electrolysis reaction) which causes need for a higher cell voltage which results in consumption of large quantities of electricity. If plant oils and animal fats are to be an economically viable source from which hydrocarbons may be produced, then the Kolbe electrolysis reaction needs to be improved in terms of its electrical usage efficiency.
In the prior art, improvements have been attempted in the Kolbe electrolysis reaction process by adding a large wt. % of acetic acid to accompany the fatty acids undergoing decarboxylation (see Weedon et al. (1952); Sumera and Sadain (1990); Meresz, U.S. Pat. No. 4,018,844 (at Col 2:lines 7-10 and in Example 7 in Table I of Col 3-4 which specifically uses acetic acid and oleic acid in a Kolbe electrolysis reaction). In the prior art, others practicing the Kolbe reaction do not add any acetic acid at all. Notable examples are the Bradin U.S. Pat. Nos. 7,928,273 and 8,481,771 which teach a production of biodiesel, gasoline and jet fuel from decarboxylation reactions of fatty acids.
Acetic acid is an expensive reagent. Added acetic acid will react in a Kolbe reaction to produce ethane, which is not liquid at room temperature and hence of less interest for particular applications. Production of ethane in this way consumes large amounts of electricity and increases operating costs. In addition, the added acetic acid will react in a Kolbe reaction with the other free fatty acids present in the reaction, such as the fatty acids obtained by hydrolysis of plant oils or animal fats. This side reaction of acetic acid with other fatty acids is Kolbe reaction hetero-coupling. It has been known that the presence of acetic acid will lower the yield of the hydrocarbons that would be produced by the Kolbe reaction process from the feedstock sources (plant oils and animal fats) used to make the fatty acid. Thus there is an important need to improve the Kolbe electrolysis reaction primary hydrocarbon yield and lower wasteful electrical usage by the Kolbe reaction process.
It is against this background that the various embodiments of the present invention were developed.